docs: def _skip_to_nonblank(f, spacegroup, setting):
      """Read lines from f until a nonblank line not starting with a
      hash (#) is encountered and returns this and the next line."""
      while True:
          line1 = f.readline()
          if not line1:
              raise SpacegroupNotFoundError(
                  'invalid spacegroup %s, setting %i not found in data base' %
                  ( spacegroup, setting ) )
          line1.strip()
          if line1 and not line1.startswith('#'):
              line2 = f.readline()
              break
      return line1, line2